1. Field of the Invention
The present invention relates generally to the field of electrical cables and connectors, and more particularly relates to impedance matching for transmission line connections.
2. Background Information
Advances in semiconductor manufacturing processes have resulted in the production of integrated circuits having many millions of transistors as well as other active and passive components. The same advances that have provided the reduction in physical dimensions necessary to integrate millions of electrical elements on a single chip, also provide dramatic increases in operating frequency for these integrated circuits. Integrated circuits implementing logic functions now commonly operate at several GHz, and an order of magnitude increase in operating frequency is expected within a few years.
As is well known, integrated circuits are commonly given a protective package, and then mounted on, or otherwise coupled to, a substrate such as a printed circuit board. In the past, when operating frequencies, sometimes referred to as operating speeds, were much lower, the primary limitation on system performance was the ability of the integrated circuits to operate at higher speeds, rather than the intra-board, or inter-board interconnection schemes. However, at very high speeds it became common to require that special attention be given to the design and implementation of those intra-board and inter-board interconnections so that the performance of electronic systems incorporating integrated circuits that operate at very high speeds would not be unduly limited by those interconnections.
When providing for the signal pathways between components which generate very high frequency signals as outputs, it is sometimes necessary to provide interconnections such as differential pairs, wave guides, or transmission lines. Transmission line characteristics may be achieved by a form of interconnection known as coaxial cables, which are more simply known as coax cables, or coax.
Coax cables typically have a center conductor surrounded by a dielectric material, an electrically conductive shield surrounding the dielectric material, and an insulator that covers the outer surface of the shield. In order to couple a coax cable to a board, a chassis, another coax cable, or any other point of electrical connection, a connector is fitted to an end of the coax cable, such that it may physically connect to, or mate with, a corresponding connector on the board, chassis, or other point. Fitting the connector to the coax cable typically involves cutting back one or more of the insulator that covers the outer surface of the shield, the electrically conductive shield, and the dielectric material, such that the center conductor extends outwardly from the end of the cable and thereby facilitates fitting of the connector to the cable. Once the two aforementioned connectors are joined, an electrical connection is formed between the coax cable and whatever other conductive media it has been joined to by the connector.
It has been observed that discontinuities in electrical characteristics, where two conductors are joined, may result in degradation in electrical performance which limits the frequency of signals that may be successfully communicated through such joined conductors. These limiting discontinuities include impedance mismatches.
What is needed are methods and apparatus for providing connectors and connection schemes suitable for reducing the impedance mismatches that limit performance in very high speed electrical systems.
Briefly, methods and apparatus are provided in accordance with the present invention in which an electrical connection between at least two conductors is obtained with very low, or zero, impedance mismatch.
In one exemplary embodiment of the present invention, reduced impedance mismatches are obtained when coupling electrical signalling media by replacing conventional connector architectures, which disrupt transmission line characteristics, with an electrical coupling means that permits the electrical signalling media to present a planar interface for interconnection. Such electrical coupling means include, but are not limited to, pressure connections which may be implemented by anisotropic conductors, C-shaped spring connectors, or any other suitable means of making an electrical connection between two substantially planar conductor surfaces.